Microsoft’s U.S. search market share was 8.4% in June, up from 8.0% in May, according to comScore.

It would have been a disaster if Bing didn’t grow at all with all that advertising and free promotion via news coverage, so at least it’s up a little. (And represents Microsoft’s best month since 8.5% share in January.) But gaining 40 basis points — especially as Google’s 65.0% share stayed steady — is not an impressive victory.

It’ll still be a few months before we know if Bing is going to be a long-term success for Microsoft. But based on this lackluster first month’s showing — and recent survey results suggesting 98% of searchers won’t switch to Bing as their primary search engine — there’s little reason to get excited.

Meanwhile, Yahoo continued to lose share, accounting for 19.6% of the U.S. search market in June, down from 20.1% in May. After having stabilised, downward momentum for Yahoo is not good, and makes a search deal with Microsoft more likely.

Boilerplate reminder/disclaimer: comScore data is just one set of information from one source, only measures the U.S., etc.